Seasonal to Decadal Patterns in Sea Ice and Turbidity at Arctic River Mouths

Abstract

Rapid warming of the Arctic is accelerating riverine delivery of freshwater, heat, and sediment to the Arctic Ocean. River mouth zones are especially vulnerable to this change, as these dynamic land–ocean interfaces are hotspots of primary productivity. Coastal sea ice breakup and sediment plume development are two seasonal processes that are directly influenced by riverine input, yet they remain under‐observed. This study examines six major Arctic river mouths to characterize the spatial and temporal variability of spring sea ice breakup and sediment plume development across sub‐seasonal to decadal timescales using MODIS satellite data. Findings indicate that river mouths follow two end‐member ice breakup regimes: shoreline‐initiated breakup progressing seaward or offshore flaw lead‐initiated breakup progressing both landward and seaward. The ice melt season—the period between initial ice‐breakup and when a system is functionally ice‐free—is shortening at Eurasian systems, while North American systems remain relatively stable. Turbid sediment plumes develop as watersheds thaw and coastal ice continues to retreat, with turbidity typically peaking in early summer and occasional late‐season resuspension events. Plume onset is occurring significantly earlier at the Lena, Kolyma, and Mackenzie, and plume area is increasing at the Ob‐Yenisei. Overall, Arctic river mouth processes are responding to rapid warming, yet the magnitude and timing of these changes vary substantially among river systems, reflecting strong local controls.